What is the where? [duplicate]

You have a collection of numbers.

List<int> numeros = new List<int>
{
   1,2,3,4,5
}

You want a new collection with just the even numbers from your otiginal list

var numPares = numeros.Where(x => x % 2 == 0).ToList();

The Where clause works as a filter for collections, in it you pass your criteria to filter a collection and receive a new filtered collection from the original collection.

See working in .NET Fiddle

Example with non-primitive type:

In the example above, I worked with a list of int (primitive type), and if it was a list of a class I created? Type a list of Pessoas ?

public class Pessoa
{
   public string Nome { get; set; }
   public int Idade { get; set; }
}

Assuming I have a populated list:

var pessoas = new list<Pessoa>();
// Popula a lista com algumas pessoas...

Let's filter:

// Pessoas Idosas
var pessoasIdosas = pessoas.Where(x => x.Idade > 60).ToList();

// Pessoas Idosas cujo nome começa com a letra "A"
var pessoasIdosasComNomeComecaLetraA = pessoas.Where(x => x.Idade > 60 && x.Nome.StartsWith("A")).ToList();

See working in .NET Fiddle

Where is a conditional clause Example: Return first car where the model is 'GOL', you can do a search on Lambda and Linq to understand more about these types of conditions.

List<Carro> carros = new List<Carro>();
carros.Where(x=>x.Modelo == "GOL").FirstOrDefault();